Optical system and optical instrument

Abstract

To provide an optical system that allows insertion and withdrawal of a magnification conversion optical group, and has a short total length.SOLUTION: An optical system consists of a front group, an aperture stop, and a rear group, which are arranged in order from an object side to an image side. The optical system has a magnification conversion optical group inserted and withdrawn between the aperture stop and an image surface to change a focal length of the optical system, and a positive lens group closer to the image side than the magnification conversion optical group. When a focal length of the positive lens group is defined as fimg, a distance on an optical axis from an optical surface on the most object side in the positive lens group to the image surface as Limg, a focal length of the magnification conversion optical group as fext, a distance on the optical axis from an optical surface on the most object side of the magnification conversion optical group inserted into the optical system to the image surface as Lext, a focal length of the optical system focused on an infinite object when the magnification conversion optical group is not inserted into the optical system as fao, and a total length of the optical system focused on the infinite object as L, a condition of 0.10≤[(|fimg×Limg|) / (|fext×Lext|)] / (L / fao)≤0.90 is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an optical system used in optical equipment such as an interchangeable lens or an imaging device. [Background technology]

[0002] One method for changing the focal length of an optical system used for imaging is to insert a magnification conversion optical group such as an extender into the optical path. Furthermore, as an optical system in which the overall length (the distance from the optical surface closest to the object to the image plane) does not change by inserting or removing a magnification conversion optical group, Patent Document 1 discloses an optical system in which a magnification conversion group can be inserted or removed at a position where an axial light beam converges between the aperture stop and the image plane. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-238827 Summary of the Invention [Problem to be solved by the invention]

[0004] However, providing a space for inserting a magnification conversion optical group between the aperture stop and the image plane as in Patent Document 1 increases the overall length of the original optical system. Also, inserting a magnification conversion optical group in a narrow space may increase various aberrations in the optical system.

[0005] The present invention provides an optical system in which a magnification conversion optical group can be inserted or removed, yet which has a short overall length and provides good optical performance. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention comprises a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side. The rear group has a magnification conversion optical group that is inserted or removed between the aperture stop and the image plane to change the focal length of the optical system, and a positive lens group consisting of all lenses arranged closer to the image side than the magnification conversion optical group. The rear group is arranged between the aperture stop and the magnification conversion optical group, and has an IS lens group that moves in a direction perpendicular to the optical axis for image blur correction. The focal length of the positive lens group is defined as f img , the distance on the optical axis from the optical surface closest to the object in the positive lens group to the image plane is L img , the focal length of the magnification conversion optical group is f ext , the distance on the optical axis from the optical surface closest to the object in the magnification conversion optical group inserted in the optical system to the image plane is L ext , the focal length of the optical system when focused on an object at infinity without the magnification conversion optical group inserted is f ao When the total length of the optical system focused on an object at infinity is L, 0.10≦[(|f img ×L img |) / (|f ext ×L ext |)] / (L / f ao )≦0.90 The optical system is characterized by satisfying the following conditions: Note that an optical device using the above optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an optical system in which a magnification conversion optical group can be inserted or removed, yet which has a short overall length and provides good optical performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1A and 1B are a cross-sectional view and longitudinal aberration diagram of the optical system of Example 1 (without inserting the magnification conversion group); [Figure 2] 1A and 1B are a cross-sectional view and longitudinal aberration diagram of the optical system of Example 1 (with the magnification conversion group inserted). [Figure 3] 10A and 10B are a cross-sectional view and longitudinal aberration diagram of the optical system of Example 2 (without the magnification conversion group inserted). [Figure 4] 10A and 10B are a cross-sectional view and longitudinal aberration diagram of the optical system of Example 2 (with the magnification conversion group inserted). [Figure 5] 10A and 10B are a cross-sectional view and longitudinal aberration diagram of the optical system of Example 3 (without the magnification conversion group inserted). [Figure 6] 10A and 10B are a cross-sectional view and longitudinal aberration diagram of the optical system of Example 3 (with the magnification conversion group inserted). [Figure 7] FIG. 1 is a diagram showing an imaging device having an optical system according to any one of Examples 1 to 3. [Figure 8] 1A and 1B are diagrams showing the configuration of a diffractive optical element in Examples 1 and 2. [Figure 9] FIG. 10 is a graph showing the wavelength dependency of the diffraction efficiency of a diffractive optical element. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0010] First, an overview of an optical system according to an embodiment of the present invention will be described. The optical system according to the embodiment is a telephoto lens optical system that serves as an interchangeable lens (optical equipment) that can be attached to and detached from an imaging device such as a video camera, a digital still camera, a silver halide film camera, or a broadcast television camera. However, the optical system according to the embodiment may also be provided integrally as an imaging lens of the imaging device.

[0011] Furthermore, the optical system of the embodiment can have a magnification conversion optical group inserted or removed, and by inserting the magnification conversion optical group, the focal length of the entire system can be changed to the long focal length side. Specifically, an optical system with a maximum half angle of view of 4.5° or less (a focal length of 300 mm or more when converted into a 35 mm full-frame image sensor) is assumed.

[0012] Generally, in a telephoto lens, from the viewpoint of securing space between the object side and the aperture stop and between the aperture stop and the image plane, and from the viewpoint of the weight when the magnification conversion optical group is inserted, it is desirable to insert and remove the magnification conversion optical group between the aperture stop and the image plane, as in the optical system disclosed in Patent Document 1. For this reason, even in the optical system of the example, the magnification conversion optical group is inserted and removed within the rear group between the aperture stop and the image plane.

[0013] In the optical system of the embodiment, the relationship between the refractive power and the arrangement of the inserted magnification conversion optical group and the lens group with positive refractive power (positive lens group) arranged closer to the image side than the inserted magnification conversion optical group in the rear group is appropriately set. Specifically, the absolute values ​​of the refractive power of the magnification conversion optical group and the positive lens group are made stronger than the absolute values ​​of the refractive power of the other lens groups. In particular, the absolute value of the refractive power of the positive lens group is made stronger. This relationship of refractive power allows the outward bending of off-axial rays associated with the long focal length by the magnification conversion optical group to be performed in a space-saving manner, and the outwardly bent off-axial rays are converged by the positive lens group on the image side, thereby shortening the overall length of the optical system (lens). The overall length of the optical system is the distance on the optical axis from the optical surface closest to the object to the image plane.

[0014] Furthermore, in the optical system of the embodiment, the distance on the optical axis from the magnification conversion optical group to the image plane and the distance on the optical axis from the positive lens group to the image plane are shortened. By shortening the latter distance in particular, the physical distance can be shortened, and therefore the overall lens length can be further shortened.

[0015] The configuration of an optical system of an embodiment and the conditions satisfied by the optical system are described below. The optical system of the embodiment has, in order from the object side to the image side, a front group, an aperture stop, and a rear group, and also has a magnification conversion optical group that can be inserted as part of the rear group between the aperture stop and the image plane to change the focal length of the optical system. The rear group has the above-mentioned positive lens group located closer to the image than the magnification conversion optical group.

[0016] In such an optical system, the focal length of the positive lens group on the image side of the magnification conversion optical group is f img , the distance on the optical axis from the optical surface in the positive lens group closest to the object to the image plane is L img, the focal length of the magnification conversion optical group is f ext The distance on the optical axis from the optical surface closest to the object in the magnification conversion optical group inserted in the optical system (rear group) to the image plane is L. ext , the focal length of the optical system when focused on an object at infinity without the magnification conversion optical group inserted is f ao The total length of the optical system when focused on an object at infinity is L. In this case, the optical system satisfies the following conditional expression (1).

[0017] 0.10≦[(|f img ×L img |) / (|f ext ×L ext |)] / (L / f ao )≦0.90 (1) Conditional expression (1) indicates the condition that must be satisfied by the refractive power and arrangement of the magnification conversion optical group in the rear group and the positive lens group to the image side of it in order to shorten the overall length of the optical system. If the value of conditional expression (1) exceeds the upper limit, the distance from the positive lens group to the image plane becomes too long, undesirably lengthening the overall length of the optical system. If the value of conditional expression (1) falls below the lower limit, the focal length of the magnification conversion optical group becomes too short (the refractive power becomes too strong), undesirably increasing sensitivity during manufacturing.

[0018] It is more preferable to set the numerical range of conditional expression (1) as follows in order to shorten the overall length of the optical system.

[0019] 0.200≦[(|f img ×L img |) / (|f ext ×L ext |)] / (L / f ao )≦0.875 (1a) Furthermore, it is even more preferable to set the numerical range of conditional expression (1) as follows in order to shorten the overall length of the optical system. 0.30≦[(|f img ×L img |) / (|f ext ×L ext |)] / (L / f ao )≦0.85 (1b) In addition to satisfying conditional expression (1), it is preferable to satisfy at least one of the following conditional expressions (2) to (4).

[0020] The focal length of the rear group when the magnification conversion optical group is inserted is f ri When this is the case, it is preferable to satisfy the following conditional expression (2):

[0021] 1.50≦(|f img / f ri |) / (L / f ao )≦3.50 (2) Conditional expression (2) is a condition that is preferably satisfied by the focal lengths of the magnification conversion optical group and the rear group in order to ensure high optical performance when the magnification conversion optical group is inserted in an optical system with a shortened overall length. If the value of conditional expression (2) exceeds its upper limit, the focal length of the magnification conversion optical group becomes too large (refractive power becomes too weak) relative to the focal length of the rear group, making it impossible to bend off-axial rays passing through the rear group outward, and the space required to insert the magnification conversion optical group becomes too large, increasing the overall length of the optical system, which is undesirable. If the value of conditional expression (2) falls below its lower limit, the focal length of the magnification conversion optical group becomes too small (refractive power becomes too strong) relative to the focal length of the rear group, making it impossible to fully correct off-axial aberrations (astigmatism) generated by the magnification conversion optical group by other lens groups, which is also undesirable.

[0022] It is more preferable to set the numerical range of conditional expression (2) as follows in order to ensure high optical performance.

[0023] 1.75≦(|f img / f ri |) / (L / f ao )≦3.25 (2a) Furthermore, it is even more preferable to set the numerical range of conditional expression (2) as follows in order to ensure high optical performance. 2.00≦(|f img / f ri |) / (L / f ao )≦3.00 (2b) The focal length of the front group is f f , the focal length of the rear group when the magnification conversion optical group is not inserted is fro , the focal length of the optical system when the magnification conversion optical group is inserted and focused on an object at infinity is f ai The focal length of the front group is f f The absolute value of is the focal length f of the rear group when the magnification conversion optical group is inserted. ri In this case, it is preferable to satisfy the following conditional expression (3):

[0024] 0.25≦(|f ri ×f ro / f f 2 |) / [L 2 / (f ai ×f ao )]≦4.00 (3) Conditional expression (3) indicates a condition that the focal lengths of the magnification conversion optical group and the front and rear groups must satisfy in order to shorten the overall length of the optical system and ensure good optical performance both when the magnification conversion optical group is inserted and when it is not. If the value of conditional expression (3) exceeds the upper limit, the focal length of the rear group becomes too long (refractive power becomes too weak) when the magnification conversion optical group is inserted, which is undesirable because it makes it difficult to correct various aberrations that occur in the front group. If the value of conditional expression (3) falls below the lower limit, the focal length of the rear group becomes too short when the magnification conversion optical group is inserted, which is undesirable because it makes it difficult to correct off-axis aberrations (astigmatism) that occur in the rear group.

[0025] Setting the numerical range of conditional expression (3) as follows is more preferable in order to shorten the overall length of the optical system and ensure good optical performance. 0.50≦(|f ri ×f ro / f f 2 |) / [L 2 / (f ai ×f ao )]≦3.75 (3a) Furthermore, it is even more preferable to set the numerical range of conditional expression (3) as follows, in order to shorten the overall length of the optical system and ensure good optical performance. 0.70≦(|f ri ×f ro / ff 2 |) / [L 2 / (f ai ×f ao )]≦3.60 (3b) The air-equivalent distance on the optical axis from the optical surface closest to the image (final optical surface) of the lens group closest to the image in the optical system to the image plane is Sk, and the maximum image height on the image plane is h. img When it is assumed that: it is preferable to satisfy the following conditional expression (4): 0.30≦[(|f img ×L img |) / (|f ext ×L ext |)] / [(h img / Sk)×(L / f ao )]≦3.00 (4) Conditional expression (4) indicates a condition that is preferably satisfied by the refractive power and arrangement of the magnification conversion optical group in the rear group and the positive lens group on the image side of it, in order to further shorten the overall length of the optical system both when the magnification conversion optical group is inserted and when it is not inserted. Conditional expression (4) satisfies the air-equivalent distance Sk on the optical axis from the final optical surface to the image plane and the maximum image height h in relation to conditional expression (1). img This conditional expression (4) can also be applied to an optical system in which the air-equivalent distance Sk on the optical axis is short.

[0026] If the value of conditional expression (4) exceeds the upper limit, the distance from the positive lens group to the image plane becomes too long, undesirably increasing the overall length of the optical system.If the value of conditional expression (4) falls below the lower limit, the focal length of the magnification conversion optical group becomes too short (the refractive power becomes too strong), undesirably increasing sensitivity during manufacturing.

[0027] It is more preferable to set the numerical range of conditional expression (4) as follows in order to shorten the overall length of the optical system. 0.40≦[(|f img ×L img |) / (|f ext ×L ext |)] / [(h img / Sk)×(L / f ao )]≦2.75 (4a) Furthermore, it is even more preferable to set the numerical range of conditional expression (4) as follows in order to shorten the overall length of the optical system. 0.50≦[(|f img ×L img |) / (|f ext ×L ext |)] / [(h img / Sk)×(L / f ao )]≦2.50 (4b) Furthermore, common features of the optical systems of the examples described below include that the overall length of the optical system does not change when the magnification conversion optical group is inserted or removed, and that the optical system is an ultra-telephoto lens with a maximum half angle of view of 4.5° or less. In particular, because the overall length does not change when the magnification conversion optical group is inserted or removed, it is possible to solve the problem of an increase in the overall length and weight of an ultra-telephoto lens as the focal length increases.

[0028] Next, specific examples will be described. First, matters common to each example will be described. The optical system in each example is a single-focus super telephoto lens. FIGS. 1, 3, and 5 show the cross sections and longitudinal aberrations of the optical systems of Examples 1, 2, and 3, respectively, when the magnification conversion optical group is not inserted and the optical system is focused on an object at infinity. FIGS. 2, 4, and 6 show the cross sections and longitudinal aberrations of the optical systems of Examples 1, 2, and 3, respectively, when the magnification conversion optical group is inserted and the optical system is focused on an object at infinity.

[0029] The optical system in each embodiment is composed of, arranged in order from the object side to the image side, a front group LF, an aperture stop S, and a rear group LR. The front group LF is composed of, arranged in order from the object side to the image side, a first lens group L1 with positive refractive power and a second lens group L2 with negative refractive power. The rear group LR is composed of, arranged in order from the object side to the image side, a third lens group L3, a fourth lens group L4 as a magnification conversion optical group with negative refractive power, and a fifth lens group (positive lens group) with positive refractive power. The overall length of the optical system remains unchanged whether the fourth lens group L4 is inserted or not.

[0030] Focusing from an object at infinity to an object at a close distance is performed by moving the focus lens group Lfo that constitutes the second lens group L2 toward the image side.

[0031] In each cross-sectional view, O represents the optical axis, IP represents the image plane, and G represents a glass block such as a quartz low-pass filter or an infrared cut filter. In Examples 1 and 2, Ldoe represents a diffractive optical element, and asph represents an aspheric surface. In both Examples 1 and 2, the diffractive surface of the diffractive optical element Ldoe is provided on the cemented surface of the second cemented lens element counting from the object side. Furthermore, the aspheric surface asph is provided on the object-side optical surface of the positive lens element closest to the object side.

[0032] In each embodiment, the IS lens group LIS in the third lens group L3 is moved in a direction perpendicular to the optical axis O to reduce (correct) image blur caused by camera shake or the like.

[0033] For spherical aberration, which is a type of longitudinal aberration, the solid line indicates spherical aberration for the d-line (wavelength 587.6 nm), the two-dot chain line indicates spherical aberration for the g-line (wavelength 435.8 nm), and the dashed line indicates the sine condition. For astigmatism, the solid line (S) indicates astigmatism for the sagittal ray of the d-line, and the dotted line (M) indicates astigmatism for the meridional ray of the d-line. Distortion indicates distortion for the d-line. Chromatic aberration indicates lateral chromatic aberration for the g-line. Fno indicates the F-number, and ω indicates the half angle of view (°).

[0034] Furthermore, after the explanation of Examples 1 to 3, numerical examples corresponding to each Example are shown. The numerical examples include a numerical example in which the magnification conversion optical group is not inserted and the lens is focused on an object at infinity, and a numerical example in which the magnification conversion optical group is inserted and the lens is focused on an object at infinity. Furthermore, Table 1 shown after Numerical Examples 1 to 6 collectively shows the values ​​of the above-mentioned conditional expressions (1) to (4) in Examples 1 to 3 (Numerical Examples 1 to 6). [Example]

[0035] 1 and 2 is an ultra-telephoto lens having a focal length of 392.6 mm and an F-number of 4.12 when the fourth lens group (magnification conversion optical group) L4 is not inserted as shown in Numerical Example 1, and a focal length of 549.7 mm and an F-number of 5.77 when the fourth lens group L4 is inserted as shown in Numerical Example 2. The fifth lens group L5, which is closest to the image side, is composed of a cemented lens.

[0036] As can be seen from the longitudinal aberration diagrams of FIGS. 1 and 2, in the optical system of this embodiment, each aberration is well corrected whether the fourth lens unit L4 is inserted or not.

[0037] Furthermore, as can be seen from Numerical Examples 1 and 2 and Table 1, the optical system of this example satisfies conditional expressions (1) to (4). Therefore, the optical system of this example has a short overall length, is excellent in optical performance with various aberrations well corrected, and allows the fourth lens unit L4 to be inserted and removed. [Example]

[0038] 3 and 4 is an ultra-telephoto lens having a focal length of 392.6 mm and an F-number of 4.12 when the fourth lens group (magnification conversion optical group) L4 is not inserted as shown in Numerical Example 3, and a focal length of 549.7 mm and an F-number of 5.77 when the fourth lens group L4 is inserted as shown in Numerical Example 4. The fifth lens group L5, which is closest to the image side, is composed of a single lens and a cemented lens.

[0039] As can be seen from the longitudinal aberration diagrams of FIGS. 3 and 4, in the optical system of this embodiment as well, each aberration is well corrected whether the fourth lens unit L4 is inserted or not inserted.

[0040] Furthermore, as can be seen from Numerical Examples 3 and 4 and Table 1, the optical system of this example also satisfies conditional expressions (1) to (4). Therefore, the optical system of this example also has a short overall length and high optical performance with various aberrations well corrected, while allowing the fourth lens unit L4 to be inserted and removed. [Example]

[0041] The optical system of Example 3 shown in Figures 5 and 6 is an ultra-telephoto lens having a focal length of 585.0 mm and an F-number of 4.12 when the fourth lens group (magnification conversion optical group) L4 is not inserted as shown in Numerical Example 5, and a focal length of 819.2 mm and an F-number of 5.77 when the fourth lens group L4 is inserted as shown in Numerical Example 6. The fifth lens group L5, which is closest to the image side, is composed of a cemented lens. Furthermore, the optical system of this example does not use a diffractive optical element or an aspherical surface, and is composed only of spherical lenses.

[0042] As can be seen from the longitudinal aberration diagrams of FIGS. 5 and 6, in the optical system of this embodiment as well, each aberration is well corrected whether the fourth lens unit L4 is inserted or not inserted. Furthermore, as can be seen from Numerical Examples 5 and 6 and Table 1, the optical system of this example also satisfies conditional expressions (1) to (4). Therefore, the optical system of this example also has a short overall length and high optical performance with various aberrations well corrected, while allowing the fourth lens unit L4 to be inserted and removed.

[0043] It should be noted that Examples 1 to 3 and Numerical Examples 1 to 6 are merely examples, and any optical system that is composed of a front group, an aperture stop, and a rear group, in which a magnification conversion optical group can be inserted or removed within the rear group, and that satisfies conditional expressions (1) to (4) is included in the examples of the present invention.

[0044] FIG. 7 shows a digital still camera (optical equipment) as an imaging device using the optical system of each embodiment as an imaging lens. 10 denotes a camera body, and 11 denotes an imaging lens configured using any of the optical systems of Embodiments 1 to 3. 12 denotes a solid-state imaging element (photoelectric conversion element) such as a CCD sensor or CMOS sensor that is built into the camera body 10 and captures an optical image formed by the imaging lens 11. By using the optical system of each embodiment in this way, a compact camera with high optical performance can be obtained. The camera body 10 may be a single-lens reflex camera with a quick-turn mirror, or a mirrorless camera without a quick-turn mirror.

[0045] Next, the diffractive optical element Ldoe used in Examples 1 and 2 will be described with reference to Fig. 8. In Examples 1 and 2, a diffractive optical element 1 having a close-contact two-layer structure in which two diffraction gratings 6 and 7 having the same grating thickness d are closely contacted with each other is used as the diffractive optical element Ldoe, as shown in Fig. 8.

[0046] The diffractive optical element 1 is fabricated as follows. First, a sawtooth-shaped first diffraction grating 6 is formed on a glass substrate (lens) 4 using a first ultraviolet-curing resin. At this time, the first diffraction grating 6 is formed so that the grating thickness monotonically increases from top to bottom in FIG. 8. Next, a sawtooth-shaped second diffraction grating 7 is formed using a second ultraviolet-curing resin different from the first ultraviolet-curing resin so as to fill in the valleys of the first diffraction grating 6. The second diffraction grating 7 is formed so that the grating thickness monotonically decreases from top to bottom in FIG. 8. Then, a glass substrate (lens) 5 is provided so as to contact the back surface of the second diffraction grating 7.

[0047] When light is incident on the diffractive optical element 1 manufactured in this manner from the glass substrate 4 side as shown in FIG. 8, first-order diffracted light traveling diagonally downward to the right and zeroth-order diffracted light traveling straight to the right are generated.

[0048] Figure 9 shows the wavelength dependence of the diffraction efficiency of the first-order diffracted light, which is the design diffraction order of the diffractive optical element 1 shown in Figure 8, and its ±1st-order diffracted lights, which are the zeroth-order diffracted light and the second-order diffracted light. Here, the refractive index nd1 of the material of the first diffraction grating 6 with respect to the d-line and the Abbe number vd1 based on the d-line are (nd1, vd1) = (1.620, 43.0), and the refractive index nd2 of the material of the second diffraction grating 7 with respect to the d-line and the Abbe number vd2 based on the d-line are (nd2, vd2) = (1.567, 19.4). The grating thickness d of the first and second diffraction gratings is d = 11.5 μm, the grating pitch P is P = 200 μm, and light is incident perpendicular to the glass substrate 4.

[0049] As can be seen from Figure 9, the diffraction efficiency of the designed diffraction order light (first-order diffracted light) is high at approximately 99.5% or more over the entire wavelength range used, and the diffraction efficiency of the unnecessary diffraction orders light (zeroth- and second-order diffracted light) is sufficiently suppressed to approximately 0.05% or less over the entire wavelength range used.

[0050] As the diffractive optical element Ldoe, a diffractive optical element having another configuration may be used as long as the basic performance such as diffraction efficiency is equivalent to that of the diffractive optical element 1 shown in FIG.

[0051] Furthermore, the diffractive optical element Ldoe is provided on an optical surface, which may be spherical, aspherical, or flat. In Examples 1 and 2, the diffractive optical element Ldoe is provided on the cemented surface of the cemented lens, but it may also be provided on another optical surface.

[0052] In addition, the diffractive optical element Ldoe can be manufactured not only by directly molding the binary optics shape onto the lens surface using photoresist, but also by replica molding or molding using a mold created by this method. Numerical Examples 1 to 6 are shown below. In each of the numerical examples, r is the radius of curvature of the ith optical surface from the object side, d is the distance on the optical axis between the ith optical surface and the (i+1)th optical surface from the object side, and nd and vd are the refractive index of the ith optical member with respect to the d-line and the Abbe number with respect to the d-line as the reference. The Abbe number vd is given by Nd, NF, and NC, respectively, where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines, respectively. νd=(Nd-1) / (NF-NC) It is expressed as:

[0053] BF represents back focus (mm). "Back focus" is the distance on the optical axis from the final surface of the optical system (the optical surface closest to the image) to the paraxial image plane, expressed as an air-equivalent length. "Total lens length" is the distance on the optical axis from the foremost lens surface of the optical system (the lens surface closest to the object) to the final surface plus the back focus, and is equivalent to the total length of the optical system.

[0054] An asterisk (*) next to a surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following equation, where X is the position in the optical axis direction, r is the height in the direction perpendicular to the optical axis, the direction of light propagation is positive, R is the paraxial radius of curvature, k is the conic constant, and B, C, D, and E are aspherical coefficients.

[0055]

number

[0056] The "ex" of the conic constant and aspherical coefficient is x10 -x means. (Numerical Example 1) Optical system in Example 1 without the magnification conversion optical group inserted Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* 91.357 15.00 1.48749 70.2 95.29 2 728.677 32.00 94.08 3 118.813 16.52 1.49700 81.5 75.02 4 (diffraction) -99.439 3.72 1.77250 49.6 73.03 5 -565.977 5.50 69.85 6 59.396 2.66 1.78590 44.2 59.35 7 36.888 14.34 1.48749 70.2 53.66 8 124.176 (variable) 49.91 9 291.188 3.71 1.80810 22.8 34.32 10 -115.914 1.80 1.83400 37.2 33.30 11 56.155 (variable) 30.74 12 (Aperture) ∞ 2.50 23.30 13 -112.493 1.30 1.84666 23.9 22.45 14 43.102 4.74 1.67300 38.1 21.99 15 -59.032 1.20 21.76 16 635.187 3.25 1.80518 25.4 24.14 17 -85.036 1.30 1.74100 52.6 23.55 18 48.132 2.34 22.60 19 -80.693 1.30 1.88300 40.8 22.57 20 824.035 4.01 22.72 21 150.563 7.50 1.58144 40.8 19.96 22 -21.969 1.80 1.59282 68.6 20.18 23 -95.873 60.05 20.38 24 57.883 1.80 1.80810 22.8 54.87 25 42.318 10.03 1.67300 38.1 53.92 26 709.249 4.87 53.84 27 ∞ 2.00 1.51633 64.1 53.36 28 ∞ (variable) 53.21 Image plane ∞ Aspheric data Front page k=1.76760e-001 B=-3.83172e-008 C=-3.74976e-014 D=-5.56572e-016 E=3.38138e-019 Surface 4 (diffractive surface) C1=-4.07993e-005 C2=3.31820e-009 C3=-4.21494e-013 C4=2.96660e-016 C5= 2.29768e-020 Various data Zoom ratio 1.00 Focal length 392.58 F-number 4.12 Half angle of view (°) 3.15 Image height 21.64 Lens total length 280.33 BF 36.01 d 8 20.01 d11 19.09 d28 36.01 Entrance pupil position 493.04 Exit pupil position -498.86 Front principal point position 597.47 Back principal point position -356.58 Lens group data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 116.83 89.75 17.66 -55.00 2 9 -82.12 5.51 3.74 0.67 3 12 139.31 109.98 114.61 147.69 Single lens data Lens starting surface focal length 1 1 212.63 2 3 110.76 3 4 -158.73 4 6 -130.67 5 7 102.15 6 9 103.02 7 10 -45.14 8 13 -36.67 9 14 37.72 10 16 93.33 11 17 -41.31 12 19 -83.18 13 21 33.51 14 22 -48.51 15 24 -205.36 16 25 66.47 17 27 0.00 (Numerical Example 2) Optical system with magnification conversion optical group inserted according to Example 1 (Surface numbers 1 to 22 are the same as in Numerical Example 1) Unit: mm Surface Data Surface number rd nd νd Effective diameter 23 -95.873 2.78 20.38 24 27.876 4.94 1.54072 47.2 20.24 25 -247.012 1.73 19.95 26 75.571 5.83 1.60342 38.0 19.44 27 -53.892 2.12 1.90366 31.3 18.46 28 34.235 5.95 17.92 29 85.021 1.80 1.88300 40.8 19.23 30 18.266 8.35 1.72047 34.7 19.32 31 -24.691 1.80 1.88300 40.8 19.83 32 56.411 2.68 20.83 33 62.523 7.83 1.61340 44.3 23.05 34 -23.935 1.80 1.59282 68.6 24.13 35 151.805 12.44 25.80 36 57.883 1.80 1.80810 22.8 54.87 37 42.318 10.03 1.67300 38.1 53.92 38 709.249 4.87 53.84 39 ∞ 2.00 1.51633 64.1 53.36 40 ∞ (variable) 53.21 Image plane ∞ Various data Zoom ratio 1.00 Focal length 549.72 F-number 5.77 Half angle of view (°) 2.25 Image height 21.64 Lens total length 280.33 BF 36.00 Lens group data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 116.83 89.75 17.66 -55.00 2 9 -82.12 5.51 3.74 0.67 3 12 -86.14 109.98 0.63 -95.17 Single lens data Lens starting surface focal length 15 24 46.62 16 26 53.03 17 27 -22.91 18 29 -26.68 19 30 15.86 20 31 -19.25 21 33 29.22 22 34 -34.74 23 36 -205.36 24 37 66.47 25 39 0.00 (Numerical Example 3) Optical system according to the second embodiment without the magnification conversion optical group inserted Unit: mm Surface Data Surface number rd nd νd Effective diameter 1* 91.582 14.95 1.48749 70.2 95.19 2 742.747 32.00 94.00 3 119.171 16.45 1.49700 81.5 75.02 4 (diffraction) -100.209 3.72 1.77250 49.6 73.04 5 -558.561 5.50 69.89 6 59.334 2.66 1.78590 44.2 59.36 7 37.011 14.15 1.48749 70.2 53.71 8 121.773 20.00 50.00 9 272.156 3.72 1.80810 22.8 34.45 10 -119.044 1.80 1.83400 37.2 33.42 11 56.289 19.15 30.84 12 (Aperture) ∞ 2.50 23.26 13 -114.040 1.30 1.84666 23.9 22.39 14 39.973 4.85 1.67300 38.1 21.91 15 -58.154 1.20 21.68 16 1305.584 3.25 1.80518 25.4 24.07 17 -84.371 1.30 1.74100 52.6 23.48 18 47.182 2.34 22.54 19 -82.311 1.30 1.88300 40.8 22.52 20 2800.154 1.78 22.67 21 147.283 7.50 1.58144 40.8 19.57 22 -20.603 1.80 1.59282 68.6 19.77 23 -103.363 56.85 19.96 24 -70.468 3.91 1.61340 44.3 46.84 25 -65.677 0.86 48.83 26 56.742 1.80 1.80810 22.8 55.36 27 42.854 10.03 1.67300 38.1 54.33 28 347.440 5.58 54.15 29 ∞ 2.00 1.51633 64.1 53.62 30 ∞ (variable) 53.46 Image plane ∞ Aspheric data Front page k=1.82862e-001 B=-4.08391e-008 C=-4.60006e-013 D=-5.35541e-016 E=3.11392e-019 Surface 4 (diffractive surface) C1=-4.10416e-005 C2=3.41465e-009 C3=-5.68815e-013 C4=3.70294e-016 C5=5.77317e-021 Various data Zoom ratio 1.00 Focal length 392.20 F-number 4.12 Half angle of view (°) 3.16 Image height 21.64 Lens total length 280.36 BF 36.11 d30 36.11 Entrance pupil position 491.44 Exit pupil position -543.48 Front principal point position 618.25 Back principal point position -356.09 Lens group data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 392.20 244.25 618.25 -356.09 Single lens data Lens starting surface focal length 1 1 212.68 2 3 111.34 3 4 -160.73 4 6 -132.11 5 7 103.42 6 9 102.92 7 10 -45.61 8 13 -34.82 9 14 35.91 10 16 98.53 11 17 -40.67 12 19 -90.54 13 21 31.60 14 22 -43.76 15 24 1201.56 16 26 -229.98 17 27 71.68 18 29 0.00 (Numerical Example 4) Optical system with magnification conversion optical group inserted according to the second embodiment (Surface numbers 1 to 22 are the same as in Numerical Example 3) Unit: mm Surface Data Surface number rd nd νd Effective diameter 23 -103.363 2.92 19.96 24 27.975 4.71 1.54072 47.2 19.84 25 -244.425 1.73 19.61 26 74.383 5.84 1.60342 38.0 19.15 27 -53.787 2.12 1.90366 31.3 18.22 28 34.452 5.93 17.73 29 86.035 1.80 1.88300 40.8 19.10 30 18.455 8.18 1.72047 34.7 19.22 31 -25.584 1.80 1.88300 40.8 19.75 32 57.150 2.61 20.74 33 62.986 8.03 1.61340 44.3 22.90 34 -22.421 1.80 1.59282 68.6 23.99 35 140.866 9.37 25.74 36 -70.468 3.91 1.61340 44.3 46.84 37 -65.677 0.86 48.83 38 56.742 1.80 1.80810 22.8 55.36 39 42.854 10.03 1.67300 38.1 54.33 40 347.440 5.58 54.15 41 ∞ 2.00 1.51633 64.1 53.62 42 ∞ (variable) 53.46 Image plane ∞ Various data Zoom ratio 1.00 Focal length 549.18 F-number 5.77 Half angle of view (°) 2.26 Image height 21.64 Lens total length 280.36 BF 36.11 Single lens data Lens starting surface focal length 15 24 46.71 16 26 52.63 17 27 -22.98 18 29 -26.94 19 30 16.14 20 31 -19.81 21 33 27.96 22 34 -32.49 23 36 1201.56 24 38 -229.98 25 39 71.68 26 41 0.00 (Numerical Example 5) Optical system according to the third embodiment with the magnification conversion optical group not inserted Unit: mm Surface Data Surface number rd nd νd Effective diameter 1 230.559 20.01 1.49700 81.5 141.99 2 -690.514 40.00 140.89 3 149.543 15.04 1.49700 81.5 116.97 4 -11301.149 2.67 115.29 5 -705.634 5.90 1.83481 42.7 114.86 6 214.504 48.21 109.14 7 107.530 14.78 1.43387 95.1 97.57 8 -10313.878 0.50 96.27 9 75.098 5.00 1.51633 64.1 86.85 10 60.268 (variable) 80.84 11 485.453 5.12 1.80518 25.4 62.47 12 -255.237 3.30 1.83481 42.7 61.66 13 130.699 (variable) 58.71 14 (Aperture) ∞ 5.00 40.09 15 152.804 2.00 1.84666 23.8 38.52 16 81.654 7.52 1.60311 60.6 37.76 17 -550.671 6.18 36.65 18 94.247 4.50 1.84666 23.8 39.16 19 -1128.324 1.65 1.60311 60.6 38.22 20 48.979 3.76 35.71 21 -139.003 1.60 1.80400 46.6 35.96 22 150.006 4.72 35.76 23 107.130 3.00 1.72000 43.7 30.30 24 2194.622 79.16 30.18 25 64.892 10.00 1.74951 35.3 45.41 26 -174.492 1.90 1.84666 23.8 44.83 27 105.215 (variable) 44.21 Image plane ∞ Various data Zoom ratio 1.00 Focal length 585.00 F-number 4.12 Half angle of view (°) 2.12 Image height 21.64 Lens total length 467.45 BF 55.50 d10 43.73 d13 76.71 d27 55.50 Entrance pupil position 1063.20 Exit pupil position -159.54 Front principal point position 56.79 Back principal point position -529.50 Lens group data Group starting plane Focal length Lens length Front principal point position Rear principal point position 1 1 264.80 152.10 37.13 -105.26 2 11 -208.49 8.42 6.25 1.56 3 14 799.79 130.98 192.62 94.19 Single lens data Lens starting surface focal length 1 1 350.31 2 3 297.09 3 5 -196.48 4 7 245.39 5 9 -667.70 6 11 208.40 7 12 -103.14 8 15 -209.83 9 16 118.43 10 18 102.91 11 19 -77.79 12 21 -89.51 13 23 156.33 14 25 64.26 15 26 -77.28 (Numerical Example 6) Optical system with magnification conversion optical group inserted according to the third embodiment (Surface numbers 1 to 23 are the same as in Numerical Example 5) Unit: mm Surface Data Surface number rd nd νd Effective diameter 24 2194.622 1.90 30.18 25 30.610 5.98 1.54072 47.2 29.99 26 2343.740 0.51 29.29 27 35.025 5.41 1.60342 38.0 27.58 28 -137.835 1.15 1.90366 31.3 26.33 29 25.510 11.87 23.96 30 174.644 0.95 1.88300 40.8 23.82 31 20.646 6.90 1.72047 34.7 23.52 32 -68.916 0.95 1.88300 40.8 23.63 33 51.617 0.91 23.89 34 39.808 6.38 1.61340 44.3 24.80 35 -30.758 1.05 1.59282 68.6 24.97 36 104.622 35.20 25.35 37 64.892 10.00 1.74951 35.3 45.41 38 -174.492 1.90 1.84666 23.8 44.83 39 105.215 (variable) 44.21 Image plane ∞ Various data Zoom ratio 1.00 Focal length 819.18 F-number 5.77 Half angle of view (°) 1.51 Image height 21.64 Lens total length 467.45 BF 55.50 Single lens data Lens starting surface focal length 14 25 57.31 15 27 46.84 16 28 -23.74 17 30 -26.59 18 31 22.79 19 32 -33.30 20 34 29.29 21 35 -39.98 22 37 64.26 23 38 -77.28

[0057] [Table 1]

[0058] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0059] LF front group LR rear group S aperture stop L4 4th lens group (magnification conversion optical group)

Claims

1. An optical system comprising a front group, an aperture stop, and a rear group, arranged in this order from the object side to the image side, the rear group includes a magnification conversion optical group that is inserted or removed between the aperture stop and an image plane in order to change the focal length of the optical system, and a positive lens group consisting of all lenses that are arranged closer to the image side than the magnification conversion optical group, the rear group is disposed between the aperture stop and the magnification conversion optical group, and includes an IS lens group that moves in a direction perpendicular to the optical axis for image blur correction; The IS lens group is composed of a cemented lens in which a positive lens A and a negative lens A are cemented together, and a negative lens B, The focal length of the positive lens group is f img , the distance on the optical axis from the optical surface in the positive lens group closest to the object to the image plane is L img , the focal length of the magnification conversion optical group is f ext , the distance on the optical axis from the optical surface closest to the object in the magnification conversion optical group inserted in the optical system to the image plane is L ext , and the focal length of the optical system when the magnification conversion optical group is not inserted and the optical system is focused on an object at infinity is f ao When the total length of the optical system in a state where the object at infinity is focused is L, 0.10≦[(|f img ×L img |) / (|f ext ×L ext |)] / (L / f ao )≦0.90 An optical system characterized by satisfying the following conditions:

2. The focal length of the rear group when the magnification conversion optical group is inserted is f ri When 1.50≦(|f img / f ri |) / (L / f ao )≦3.50 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. The focal length of the front group is f f , the focal length of the rear group when the magnification conversion optical group is not inserted is f ro , the focal length of the optical system when the magnification conversion optical group is inserted and focused on the object at infinity is f ai and the focal length of the front group is f f The absolute value of the focal length f of the rear group when the magnification conversion optical group is inserted ri When it is greater than the absolute value of 0.25≦(|f ri ×f ro / f f ２ |) / [L ２ / (f ai ×f ao )]≦4.00 3. The optical system according to claim 1, wherein the following condition is satisfied:

4. The air-equivalent distance on the optical axis from the optical surface closest to the image side of the lens group closest to the image side in the optical system to the image plane is Sk, and the maximum image height on the image plane is h img When you use 0.30≦[(|f img ×L img |) / (|f ext ×L ext |)] / [(h img / Sk)×(L / f ao )] ≦３．００ 4. The optical system according to claim 1, wherein the following condition is satisfied:

5. 5. The optical system according to claim 1, wherein the overall length of the optical system does not change when the magnification conversion optical group is inserted or removed.

6. 6. The optical system according to claim 1, wherein the maximum half angle of view of the optical system is 4.5[deg.] or less.

7. The front group is composed of a first lens group L1 having a positive refractive power and a second lens group L2 having a negative refractive power, arranged in this order from the object side to the image side, 7. The optical system according to claim 1, wherein the rear group comprises, arranged in this order from the object side to the image side, a third lens group, a fourth lens group having negative refractive power as the magnification conversion optical group, and a fifth lens group as the positive lens group.

8. An optical instrument comprising the optical system according to any one of claims 1 to 7.

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